MONDAY, Nov. 28, 2016 (HealthDay News) -- Does it help to know that a double quarter-pounder with cheese delivers 740 calories? Probably not, a new study suggests.

Starting next May, fast-food chains with more than 20 locations in the United States must display calorie counts on menus. But this study questions whether the well-intended regulations will actually steer customers to less-fattening foods.

Research in Philadelphia, where such rules already exist, indicate as few as 8 percent of fast-food eaters make healthy choices based on menu calorie counts, the study found.

"I believe menu labeling has been an important policy effort to combat a public health problem for which we have few solutions," said study author Andrew Breck.

"The success of such a calorie-labeling campaign, however, requires that target consumers simultaneously see the calorie labels, are motivated to eat healthfully, and understand how many calories they should be eating," said Breck. He is a doctoral candidate at NYU Wagner Graduate School of Public Service in New York City.

Simply presenting calorie information is not enough, he and his colleagues stressed.

To be effective, nutrition labeling must be clearer and larger. It must also reach regular fast-food eaters -- people who expressed more concern with cost and convenience than nutrition, Breck and his colleagues found.

The trend toward nutrition labeling on fast-food menus began in response to the U.S. obesity epidemic. About 38 percent of adults and 17 percent of teenagers are obese, according to the U.S. Centers for Disease Control and Prevention. Obesity has been linked to a greater risk of high blood pressure, stroke, diabetes, cancer, and other health issues.

Philadelphia in 2010 required fast-food restaurants to post the caloric, fat and sodium content of meals. New York City and Seattle already had similar rules.

But based on interviews with 1,400 people in Philadelphia, Breck's team concluded that significant labeling improvements are needed for such laws to have an impact.

The researchers analyzed responses from about 700 customers at 15 fast-food eateries in Philadelphia and another 700 people interviewed by phone.

Nutrition postings went unnoticed by nearly two-thirds surveyed at the restaurants and one-third questioned by phone, the investigators found.

To increase visibility of calorie content, the study authors recommended increasing the type size or color contrast of calorie information on menus and menu boards.

Making these numbers more apparent could have another effect as well, the researchers suggested.

"We are hopeful that highly visible posting of calorie content on menus may also cause some restaurants to add new, more healthful options to their menus," Breck said.

But customers must first know what their recommended caloric intake should be -- and many don't, the study found.

Less than half of those surveyed at the restaurants correctly estimated the number of calories they should consume daily, Breck said.

To put calorie content into perspective, Breck would like to see statements like this on fast-food menu boards: "2,000 calories a day is used for general nutrition advice, but calorie needs vary."

"Traffic-light or stop-sign type labeling indicating the healthfulness of food items is another example of a policy that has proven successful in laboratory settings in improving consumer choice," Breck said. But whether it would work in real-world settings isn't yet known.

Finally, Breck said, successful nutrition labeling must provide information that differs from consumers' expectations of how many calories foods contain.

Connie Diekman, director of university nutrition at Washington University in St. Louis, said calorie posts are just a start in improving the nation's eating behaviors.

"Awareness is the first step in the change process, so if consumers begin to see the numbers, eventual change is possible," Diekman said.

Motivation is also critical, she said, "and achieving that requires time, education, a desire to change, and an environment that supports the changed behaviors."

As a society, Diekman added, "we have a ways to go to provide an environment that encourages and supports healthy eating."

The study was published online recently in the Journal of Public Policy & Marketing.